def isLeapYear(year)
    return year % 400 == 0 or (year % 4 == 0 and year % 100 != 0)
 
 
count = 0
for n in range(1900, 2021)
    if isLeapYear(n) 
        print(n, end='t')
        count += 1
        if count % 5 == 0
            print()